The purpose of the study was to determine whether uniform intramuscular heating is achieved throughout a treatment area 2 times the transducer head at both 1 and 3 MHz. Seven male and three female subjects (Age: 23.6 ± 1.0 yrs, Weight: 83.8 ± 23.2 kg, Site Skinfold: 13.9 ± 7.3 mm) underwent two ultrasound treatments (1 and 3 MHz) in the triceps surae muscle group. Thermocouples were inserted at the midpoint and periphery of the treatment area. Ten minute baseline temperatures were recorded followed by a ten minute ultrasound treatment. Two (site) X 10 (time) repeated measures ANOVAs were separately used to determine significance for 1 and 3 MHz treatments. Post-hoc testing was performed using the Bonferroni adjustment. A significant site-by-time interaction was observed for both the 1 and 3 MHz treatments. From baseline to the end of the treatment, temperature increased approximately 2.62°C and 1.58°C for the midpoint and periphery of the 1 MHz treatment and 5.88°C and 3.64°C for the 3 MHz treatment. The differences in temperature suggest that uniform heating does not occur throughout the treatment area.

• 3 MHz is more effective in raising intramuscular temperature within ERA.

• Stroke count/rate of transducer may play a factor in heating tissue.

• Treatment size may alter uniform heating.